terence114 wrote:
Unfortunately with my experience I do not understand how to create these files.
You do not need to create these files. They are created by the Windows Installer during the installation process.
Would I be able to store all my files on an external HDD that has previously been used to back up Windows programme and files etc.
You cannot install Windows on an external disk, so the OS must be on the internal disk. An external disk, however can be used to store files and applications, which are unrelated to the OS. This external disk should be formatted as NTFS for try Windows side to be able to read/write such files.
Alternatively what are my choices available
1/ purchase a new Internal HDD (Expensive)?
You can run Mac OSX from an external disk and use the entire internal disk for Windows, if that is an option you want to explore further. A minimal OSX version can run from an external USB flash drive which is about 16GB in size. Please see OS X: Installing OS X on an external volume - Apple Support for this option.